All solid fluoride ion battery

ABSTRACT

An object of the present disclosure is to provide an all solid fluoride ion battery that has a favorable capacity property. The present disclosure achieves the object by providing an all solid fluoride ion battery comprising: a cathode layer, an anode layer, and a solid electrolyte layer formed between the cathode layer and the anode layer; wherein the anode layer includes a metal fluoride containing an M1 element, an M2 element, and a F element; the M1 element is a metal element that fluorination and defluorination occur at a potential, versus Pb/PbF 2 , of −2.5 V or more; the M2 element is a metal element that neither fluorination nor defluorination occur at a potential, versus Pb/PbF 2 , of −2.5 V or more; and the M2 element is a metal element that, when in a form of a fluoride, fluoride ion conductivity is 1×10 −4  S/cm or more at 200° C.

TECHNICAL FIELD

The present disclosure relates to an all solid fluoride ion batteryhaving a favorable capacity property.

BACKGROUND ART

As high-voltage and high-energy density batteries, for example, Li ionbatteries are known. The Li ion battery is a cation-based batteryutilizing: the reaction between a Li ion and a cathode active material;and the reaction between a Li ion and an anode active material.Meanwhile, as anion-based batteries, all solid fluoride ion batteriesutilizing the reaction of a fluoride ion are known.

For example, Non-patent Literature 1 discloses an all solid fluoride ionbattery comprising an anode using an anode mixture in which an activematerial (such as BiF₃ and CuF₂), a solid electrolyte, and an electronconductive material are mixed. For example, Non-patent Literature 1discloses an anode mixture in which La_(0.9)Ba_(0.1)F_(2.9) as a solidelectrolyte and acetylene black as an electron conductive material aremixed with BiF₃. Also, for example, Patent Literature 1 discloses atechnique of adding polymer or glass that inhibits destruction of abattery due to the expansion and contraction of an electrode, to atleast one of a cathode, a solid electrolyte, and an anode of an allsolid fluoride ion battery.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 5517451

Non-Patent Literature

-   Non-patent Literature 1: M. A. Reddy et al, “Batteries based on    fluoride shuttle”, Journal of Material Chemistry 21 (2011), p.    17059-17062

SUMMARY OF DISCLOSURE Technical Problem

Associated with the recent enhancement of battery performance, furtherimprovement in the capacity property of a battery is required. Thepresent disclosure has been made in view of the above circumstances, anda main object thereof is to provide an all solid fluoride ion batteryhaving a favorable capacity property.

Solution to Problem

The accumulation of researches in order to achieve the object have ledthe present inventor to acquire knowledge that an all solid fluoride ionbattery having a favorable capacity property may be obtained by using ametal fluoride containing specific metal elements, for an anode layer.The present disclosure is an invention based on the knowledge.

The present disclosure provides an all solid fluoride ion batterycomprising: a cathode layer, an anode layer, and a solid electrolytelayer formed between the cathode layer and the anode layer; wherein theanode layer includes a metal fluoride containing an M1 element, an M2element, and a F element; the M1 element is a metal element thatfluorination and defluorination occur at a potential, versus Pb/PbF₂, of−2.5 V or more; the M2 element is a metal element that neitherfluorination nor defluorination occur at a potential, versus Pb/PbF₂, of−2.5 V or more; and the M2 element is a metal element that, when in aform of a fluoride, fluoride ion conductivity is 1×10⁻⁴ S/cm or more at200° C.

According to the present disclosure, since the anode layer includes themetal fluoride containing the M1 element, the M2 element, and the Felement, the anode layer may be formed, upon charge, in a state wherethe metal of the M1 element (active material) and the metal fluoride(solid electrolyte) containing the M2 element and the F element aredispersed at an atomic level. Meanwhile, an all solid fluoride ionbattery having a favorable capacity property may be obtained since: themetal of the M1 element has high electron conductivity; the metalfluoride containing the M2 element and the F element has high fluorideion conductivity; and further, the both are dispersed at an atomiclevel.

In the disclosure, the metal fluoride preferably has a compositionrepresented by M1_(x)M2_((1-x))F_(y), in which 0.75≤x≤0.95 and y is areal number more than 0.

The present disclosure provides an all solid fluoride ion batterycomprising: a cathode layer, an anode layer, and a solid electrolytelayer formed between the cathode layer and the anode layer; wherein theanode layer includes a metal of an M1 element, and a metal fluoridecontaining an M2 element and a F element, in which the metal of the M1element and the metal fluoride are dispersed at an atomic level; the M1element is a metal element that fluorination and defluorination occur ata potential, versus Pb/PbF₂, of −2.5 V or more; the M2 element is ametal element that neither fluorination nor defluorination occur at apotential, versus Pb/PbF₂, of −2.5 V or more; and the metal fluoridecontaining the M2 element and the F element has fluoride ionconductivity of 1×10⁻⁴ S/cm or more at 200° C.

According to the present disclosure, since: the anode layer includes themetal of the M1 element and the metal fluoride containing the M2 elementand the F element; and the metal of the M1 element and the metalfluoride are dispersed at an atomic level, an all solid fluoride ionbattery having a favorable capacity property may be obtained.

In the disclosure, the M1 element is preferably a metal element thatfluorination and defluorination occur at a potential, versus Pb/PbF₂, of−1.5 V or less. The reason therefor is to increase the battery voltage.

In the disclosure, the M1 element preferably contains at least one of aLa element and a Ce element.

In the disclosure, the M2 element preferably contains metal elements oftwo kinds or more.

In the disclosure, the M2 element preferably contains at least one kindof a Ca element, a Ba element, a Li element, a Sr element, and a Yelement.

Advantageous Effects of Disclosure

The all solid fluoride ion battery of the present disclosure exhibitseffects such that a favorable capacity property may be obtained.

BRIEF DESCRIPTION OF DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIGS. 1A to 1C are schematic cross-sectional views each showing anexample of the all solid fluoride ion battery of the present disclosure.

FIGS. 2A and 2B are schematic cross-sectional views explaining thecharging reaction of an all solid fluoride ion battery using LaF₃.

FIGS. 3A and 3B are schematic cross-sectional views explaining thecharging reaction of the all solid fluoride ion battery of the presentdisclosure.

FIG. 4 is a schematic cross-sectional view explaining the chargingreaction of an all solid fluoride ion battery usingLa_(0.9)Ba_(0.1)F_(2.9).

FIG. 5 is a schematic cross-sectional view explaining the chargingreaction of an all solid fluoride ion battery using an anode mixture.

FIG. 6 is a schematic cross-sectional view showing the constitution ofthe measurement cell obtained in Example 1.

FIG. 7 shows the charging and discharging curves in Examples 1 and 2,and Comparative Examples 1 to 3.

FIG. 8 is the results of XRD measurements in Example 2.

FIGS. 9A to 9E are the results of XPS measurements in Example 2.

DESCRIPTION OF EMBODIMENTS

The all solid fluoride ion battery of the present disclosure will behereinafter described in detail.

FIGS. 1A to 1C are schematic cross-sectional views each exemplifying theall solid fluoride ion battery of the present disclosure. FIG. 1A showsthe initial state (the state before charge), FIG. 1B shows the stateafter charge, and FIG. 1C shows the state after discharge. All solidfluoride ion battery 10 shown in FIGS. 1A to 1C each comprises cathodelayer 1, anode layer 2, solid electrolyte layer 3 formed between cathodelayer 1 and anode layer 2, cathode current collector 4 for collectingcurrents of cathode layer 1, and anode current collector 5 forcollecting currents of anode layer 2.

In all solid fluoride ion battery 10 shown in FIG. 1A, anode layer 2includes a metal fluoride (M1M2F) containing an M1 element, an M2element, and a F element. Upon charge of all solid fluoride ion battery10, the defluorination reaction of the metal fluoride (M1M2F) occurs,and thereby, as shown in FIG. 1B, the metal of the M1 element (M1) and ametal fluoride (M2F) containing the M2 element and the F element, areformed in a state that they are dispersed at an atomic level. Here, whenthe M1 element is a metal element of one kind, the metal of the M1element (M1) is a metal simple substance (M1 simple substance), and whenthe M1 element includes two kinds or more of metal elements, the metalof the M1 element (M1) is an alloy (M1 alloy). The metal of the M1element (M1) corresponds to the anode active material in the chargedstate. Meanwhile, the metal fluoride (M2F) has the specific fluoride ionconductivity, and corresponds to the solid electrolyte. Incidentally,the F element content in M2F will be less than the F element content inM1M2F since defluorination reaction occurs upon charge; however, theexpressions of M2F and M1M2F do not intend to express the F elementcontent quantitatively.

When all solid fluoride ion battery 10 shown in FIG. 1B is discharged,the fluorination reaction occurs to the metal of the M1 element (M1) soas to form the fluoride of the M1 element (M1F), as shown in FIG. 1C.This fluoride of the M1 element (M1F) corresponds to the anode activematerial in the discharged state. Meanwhile, the metal fluoride (M2F)containing the M2 element and the F element, does not react upondischarge so as to be present as the solid electrolyte.

According to the present disclosure, since the anode layer includes themetal fluoride containing the M1 element, the M2 element, and the Felement, the anode layer may be formed, upon charge, in a state wherethe metal of the M1 element (active material) and the metal fluoride(solid electrolyte) containing the M2 element and the F element aredispersed at an atomic level. Meanwhile, an all solid fluoride ionbattery having a favorable capacity property may be obtained since: themetal of the M1 element has high electron conductivity; the metalfluoride containing the M2 element and the F element has high fluorideion conductivity; and further, the both are dispersed at an atomiclevel.

Particularly in the present disclosure, the charged anode layerincludes: a metal of an M1 element; and a metal fluoride containing anM2 element and a F element, and has a configuration in which the bothare dispersed at an atomic level. In such an anode layer, extremelyfavorable electron conductive path and fluoride ion conductive path areformed so as to promote the electrode reaction; thus, an all solidfluoride ion battery having a favorable capacity property may beobtained. The reason for the both to be dispersed at an atomic level isbecause desorption of a fluoride ion from the metal fluoride (M1M2F)occurs upon charge, whereas the M1 element and the M2 element that aremetal elements (cations) do not move.

Also, in the present disclosure, since it is possible to disperse themetal of the M1 element (M1) and the metal fluoride (M2F) containing theM2 element and the F element at an atomic level, it is possible toensure fluoride ion conductivity even though the proportion of the metalfluoride (M2F), in other words, the solid electrolyte in the anode layeris low. Therefore, the proportion of the metal of the M1 element (M1),in other words, the anode active material in the anode layer may beincreased so as to increase the anode layer capacity. Thus, the presentdisclosure allows the anode layer capacity property to be favorable.

In the present disclosure, the metal of the M1 element (M1) and themetal fluoride (M2F) are formed (phase split) from the metal fluoride(M1M2F) upon charge. Specifically, since the M1 element has higherfluorination potential and defluorination potential than the potentialsof the M2 element, when the potential of the anode layer is lowered uponcharge, the metal of the M1 element (M1) is generated from the metalfluoride (M1M2F), and the metal fluoride (M2F) remains.

Compared to an anode layer using a metal fluoride (such as LaF₃)containing one kind of metal element, the capacity property of a batterymay be improved dramatically with the anode layer in the presentdisclosure. Here, the reason why sufficient capacity property cannot beobtained in a battery using the above mentioned anode layer, is presumedas follows. Hereinafter, an example when LaF₃ is used as the anode layerwill be explained. Here, ideally, the defluorination reaction of LaF₃upon charge proceeds evenly in the thickness direction of anode layer 2from anode current collector 5 side. However, as shown in FIG. 2A, thedefluorination reaction actually proceeds unevenly in the thicknessdirection of anode layer 2 from anode current collector 5 side, and Lasimple substance (La) is generated unevenly (locally). Also, as shown inFIG. 2B, a state that LaF₃ is left behind among the La simple substance,is presumed to occur because of the proceeded uneven reaction. It ispresumed that no further charging reaction is possible for LaF₃ sincethe fluoride ion conductive path to LaF₃ surrounded by the La simplesubstance, is cut off. Thus, it is presumed that the charging capacityis lowered since unreacted LaF₃ remains in the anode layer. Also, it ispresumed that discharging capacity is lowered associated with the above.

On the other hand, the anode layer in the present disclosure includes ametal fluoride containing an M1 element, an M2 element, and a F element.Hereinafter, an example when a LaCaBaF compound (M1=La, M2=Ca and Ba) isused as the metal fluoride will be explained. In the present disclosure,as shown in FIG. 3A, La simple substance (La) and CaBaF compound (suchas CaBaF₄) are formed from the LaCaBaF compound upon charge, in a highlydispersed state. Therefore, as shown in FIG. 3A, even whendefluorination reaction occurs unevenly, fluoride ions may be providedto an unreacted metal fluoride (the LaCaBaF compound). Thus, as shown inFIG. 3B, it is presumed that the unreacted metal fluoride (the LaCaBaFcompound) is not likely to be remained in anode layer 2. Therefore,favorable charging capacity and discharging capacity are presumed to beobtained.

Incidentally, as shown in the later described Comparative Example 2(FIG. 4), when the fluoride ion conductivity of the obtained metalfluoride is low, in other words, when the obtained metal fluoride doesnot function as the solid electrolyte, favorable capacity property isnot obtained even when La (metal simple substance) and BaF₂ (metalfluoride) are formed from La_(0.2)Ba_(0.1)F_(2.9) in the anode layer. Inthis case, it is presumed that the metal fluoride functions as aninsulant. In other words, in the present disclosure, since the metalfluoride containing the M2 element and the F element has the specificfluoride ion conductivity, and functions as the solid electrolyte, anall solid fluoride ion battery having a favorable capacity property maybe obtained.

Further, the anode layer using an anode mixture, in which a powder shapeanode active material and a powder shape solid electrolyte are mixed,will also be considered. As shown in FIG. 5, when the anode mixture isused, it is presumed that, since powder shape solid electrolyte 3 a isadded, the fluoride ion conductive path may be suppressed from being cutoff even when the defluorination reaction occurs unevenly. However, inthe anode layer using the anode mixture, with a small amount of solidelectrolyte, it is difficult to secure the fluoride ion conductive pathfor the entire anode layer. Also, when the solid electrolyte is added tosuch an extent that the fluoride ion conductive path for the entireanode layer may be secured, there is a concern that the anode layercapacity itself is lowered since the portion of the anode activematerial in the anode layer will relatively be less. Further, there is aconcern that the anode layer capacity itself is lowered since, in theanode mixture, a conductive material is added in many cases in order tosecure the electron conductivity. Meanwhile, in the present disclosure,the anode layer may be formed upon charge, in a state where the metal ofthe M1 element (active material) and the metal fluoride (solidelectrolyte) containing the M2 element and the F element are dispersedat an atomic level. As the result, the proportion of the metal of the M1element (active material) in the anode layer may be increased so thatthe anode layer capacity may be increased.

The all solid fluoride ion battery of the present disclosure will behereinafter described in each constitution.

1. Anode Layer

The anode layer in the present disclosure includes a metal fluoride.Further, the anode layer may or may not include a conductive materialother than the metal fluoride; however, the latter is preferable. Thereason therefor is to achieve higher capacity.

(1) Metal Fluoride

The metal fluoride preferably contains an M1 element, an M2 element, anda F element.

(i) M1 Element

The M1 element is a metal element that fluorination and defluorinationthereof occur at higher potentials (with higher fluorination anddefluorination potentials) than the potentials of the later described M2element. The fluorination and defluorination potentials versus Pb/PbF₂of the M1 element are usually −2.5 V or more, may be −2.4 V or more, andmay be −2.3 V or more. Also, the fluorination and defluorinationpotentials versus Pb/PbF₂ of the M1 element are, for example, −1.5 V orless, may be −1.6 V or less, and may be −1.7 V or less.

Here, “potentials at which fluorination and defluorination of a metalelement occur” refer to the fluorination and defluorination potentialsof the metal element in an electrochemical meaning. Specifically, the“potentials at which fluorination and defluorination of a metal elementoccur” are thermaldynamic values determined from the equilibriumreaction (M+F⁻↔MF+e⁻) of a metal element (M element) and a F element,and are intrinsic values for each metal element.

In the all solid fluoride ion battery of the present disclosure, it ispresumed that, since the F element directly reacts with the metalelement upon charge and upon discharge, the fluorination reaction anddefluorination reaction in the metal element occur, in theory, at thesame potential, in other words, at a potential determined by the abovementioned equilibrium reaction.

The “potentials at which fluorination and defluorination of a metalelement occur” may be measured by using, for example, cyclic voltammetry(CV).

Examples of the M1 element may include at least one kind of lanthanoidelements such as a La element, a Ce element, a Pr element, a Nd element,a Sm element, a Eu element, a Gd element, a Tb element, a Dy element, aHo element, an Er element, a Tm element, an Yb element, and a Luelement; an Al element, a Be element, a Mg element, a Na element, a Kelement, a Rb element, a Cs element, a Sc element, a Th element, a Hfelement, a Ti element, and a Zr element. The M1 element may be only onekind of the metal element, and may include two kinds or more of themetal elements; in the present disclosure, more preferably includes atleast one of a La element and a Ce element. The proportion of the Laelement among all the M1 elements may be 50 mol % or more, may be 70 mol% or more, may be 90 mol % or more, and may be 100 mol % (La elementonly). The proportion of the Ce element among all the M1 elements, andthe proportion of the La element and the Ce element among all the M1elements are the same as the above mentioned proportion.

As mentioned above, the M1 element becomes the metal of the M1 element(M1 simple substance, M1 alloy) after charge.

(ii) M2 Element

The M2 element is a metal element that fluorination and defluorinationthereof occur at lower potentials than the potentials of the M1 element.In other words, neither fluorination nor defluorination of the M2element occur at the fluorination and defluorination potentials of theM1 element. Specifically, the M2 element is a metal element that neitherfluorination nor defluorination thereof occur at the potential versusPb/PbF₂ of −2.5 V or more. The fluorination and defluorinationpotentials versus Pb/PbF₂ of the M2 element are usually less than −2.5V, may be −2.7 V or less, and may be −2.8 V or less. Also, thefluorination and defluorination potentials versus Pb/PbF₂ of the M2element are, for example, −3.5 V or more. Also, the differences of thefluorination and defluorination potentials between the M1 element andthe M2 element are, for example, preferably 0.05 V or more, and morepreferably 0.1 V or more.

Also, the M2 element is a metal element that, when in a form of afluoride, fluoride ion conductivity is 1×10⁻⁴ S/cm or more at 200° C.More specifically, the M2 element is a metal element that, when in aform of a metal fluoride (M2F) containing the M2 element and the Felement, the predetermined fluoride ion conductivity may be obtained.For example, in the later described Example, the fluoride ionconductivity of Ca_(1-x)Ba_(x)F₂, in which 0<x<1, was 1×10⁻⁴ S/cm ormore at 200° C. The fluoride ion conductivity at 200° C. may be 5×10⁻⁴S/cm or more, and may be 1×10⁻³ S/cm or more.

The fluoride ion conductivity refers to a fluoride ion conductivity ofthe fluoride (M2F) of the M2 element specified in the anode layer, inthe form of a pressure powder molded body. Specific measuring method isas follows: first, 200 mg of fluoride (M2F) powder is filled into aMacor ceramic tube with diameter of 10 mm, and is subjected to uniaxialpressure molding under 1 ton/cm² to mold the fluoride into a pellet;after that, acetylene black (current collector) is stacked on both sidesof the pellet, and pressed under pressure of 4 ton/cm²; the pressedstacked body is fastened with bolts under torque of 6 N·m to obtain anevaluation cell. An alternating current impedance measurement is carriedout in measurement environment of under a vacuum of 10⁻³ Pa and at 200°C.; and at frequency within a range of 10⁶ Hz to 10⁻² Hz and voltagemagnitude of 50 mA. Thereby, fluoride ion conductivity at 200° C. may beobtained.

Examples of the metal element of the M2 element may include at least onekind of a Ca element, a Ba element, a Li element, a Sr element, and a Yelement. The M2 element may be only one kind of the metal element, andmay include two kinds or more of the metal elements; however, the latteris more preferable. When the M2 element includes two kinds or more ofthe metal elements, preferable combinations may include a Ca element anda Ba element.

(iii) Metal Fluoride

The metal fluoride preferably contains an M1 element, an M2 element, anda F element. The metal fluoride is usually a solid solution. The metalfluoride contains at least the M1 element and the M2 element as themetal elements; may contain only the M1 element and the M2 element; ormay further contain an additional metal elements; however, the former ispreferable. The total proportion of the M1 element and the M2 elementamong all the metal elements in the metal fluoride is, for example, 90mol % or more. Meanwhile, the proportion of the M1 element with respectto the total of the M1 element and the M2 element is, for example,preferably 75 mol % or more, and more preferably 80 mol % or more. Also,the proportion of the M1 element is, for example, 95 mol % or less.

The metal fluoride preferably has a composition represented by, forexample, M1_(x)M2_((1-x))F_(y), in which 0.75≤x≤0.95 and y is a realnumber more than 0. Here, the value of x is preferably 0.75 or more, andmay be 0.8 or more. Also, the value of x is, for example, 0.95 or less.

Also, the value of y is usually a real number more than 0, andpreferably determined stoichiometrically according to the valence of theM1 element and the M2 element in the metal fluoride. The value of y maybe, for example, more than 2, may be 2.5 or more, and may be 2.75 ormore. Also, the value of y may be, for example, less than 3, may be 2.95or less, and may be 2.9 or less.

In an X-ray diffraction measurement of the metal fluoride using a CuKαray, a peak is preferably observed at a position of 2θ=24.20°±0.50°,24.80°±0.50°, 27.64°±0.50°, 34.90°±0.50°, 43.63°±0.50°, 44.71°±0.50°,49.50°±0.50°, 50.48°±0.50°, and 52.41°±0.50°. These peak positions arepeak positions based on the later describedLa_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9), and by setting the range of ±0.50°, acrystal phase similar to that of La_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9) maybe determined. Also, the range of the peak position may be ±0.30°, andmay be ±0.10°.

Meanwhile, the anode layer after charge, for example, includes the metalof the M1 element (M1), and the metal fluoride (M2F) containing the M2element and the F element, in which the metal of the M1 element (M1) andthe metal fluoride (M2F) are dispersed at an atomic level. Beingdispersed at an atomic level may be confirmed by, for example, anobservation with a transmission electron microscope (TEM). When theanode layer includes the metal of the M1 element, and the metal fluoridecontaining the M2 element and the F element, the proportion of the M1element with respect to the total of the M1 element and the M2 elementis, for example, preferably 75 mol % or more, and more preferably 80 mol% or more. Also, the proportion of the M1 element is, for example, 95mol % or less.

Examples of a method for preparing the metal fluoride may include, amethod in which raw materials being an M1 element source, an M2 elementsource, and a F element source are mixed and heat treated. Examples ofthe M1 element source may include a metal fluoride containing the M1element. Examples of the M2 element source may include a metal fluoridecontaining the M2 element. The heat treatment temperature is, forexample, preferably within a range of 800° C. to 1100° C., and morepreferably within a range of 900° C. to 1000° C. Examples of a heattreatment atmosphere may be under an inert gas (such as Ar gas)atmosphere.

(2) Anode Layer

The anode layer in the present disclosure includes the above mentionedmetal fluoride. The main component of the anode layer is preferably themetal fluoride containing the M1 element, the M2 element, and the Felement. The content of the metal fluoride in the anode layer is, forexample, 70% by weight or more, may be 90% by weight or more, and may be100% by weight. Also, the anode layer preferably includes the metal ofthe M1 element and the metal fluoride containing the M2 element and theF element as the main component. The total content of the metal of theM1 element and the metal fluoride in the anode layer is, for example,70% by weight or more, may be 90% by weight or more, and may be 100% byweight.

The thickness of the anode layer varies greatly with the batteryconstitution, and thus is not particularly limited.

2. Cathode Layer

The cathode layer in the present disclosure is a layer containing acathode active material of which fluorination reaction occurs upondischarge, and defluorination reaction occurs upon charge. The cathodeactive material is a material that fluorination and defluorinationthereof occur at higher potentials than the potentials of the M1 elementin the anode layer. Specifically, the fluorination and defluorination ofthe cathode active material preferably occur at a potential versusPb/PbF₂ of 0 V or more.

Examples of the cathode active material may include a metal activematerial containing a metal element, and a carbon active materialincluding a carbon element. Examples of the metal active material mayinclude a metal simple substance and an alloy including a metal elementthat fluorination and defluorination thereof occur at higher potentialsthan the potentials of the M1 element. Examples of the metal elementused for the metal active material may include at least one kind of a Pbelement, a Cu element, a Ag element, a Mn element, an Fe element, a Nielement, a Co element, a W element, a Bi element, a Sn element, a Auelement, a Pt element, a Mo element, a Cr element, a Pd element, and aTl element. When the metal active material is an alloy, among aplurality of the metal elements, a metal element with the highestfluorination potential and defluorination potential (hereinafterreferred to as metal element A) is preferably the main component of thealloy. The proportion of metal element A in the alloy may be 50 mol % ormore, may be 70 mol % or more, and may be 90 mol % or more. Also,examples of the carbon active material may include graphite andgraphene.

Examples of the shape of the cathode active material may include agranular shape and a film shape.

The thickness of the cathode layer varies greatly with the batteryconstitution, and thus is not particularly limited. Further, the cathodelayer may also provide a function as a cathode current collector.

3. Solid Electrolyte Layer

The solid electrolyte layer in the present disclosure is a layer formedbetween the cathode layer and the anode layer, and including a solidelectrolyte.

The reduction potential of the solid electrolyte used for the solidelectrolyte layer is lower than the fluorination and defluorinationpotentials of the M1 element. The reduction potential versus Pb/PbF₂ ofthe solid electrolyte is usually −2.5 V or less, may be −2.7 V or less,and may be −2.8 V or less. Also, the reduction potential versus Pb/PbF₂of the solid electrolyte may be, for example, −3.5 V or more. Thereduction potential of the solid electrolyte may be measured by using,for example, cyclic voltammetry (CV).

The fluoride ion conductivity of the solid electrolyte at 200° C. ispreferably 1×10⁻⁴ S/cm or more, may be 5×10⁻⁴ S/cm or more, and may be1×10⁻³ S/cm or more. The fluoride ion conductivity of the solidelectrolyte may be measured by using an alternating current impedancemethod. Examples of such solid electrolyte may include a metal fluoride(M2F) containing the M2 element and the F element.

Also, the thickness of the solid electrolyte layer in the presentdisclosure varies greatly with the battery constitution, and thus is notparticularly limited.

4. Other Constitutions

The all solid fluoride ion battery of the present disclosure comprisesat least the above mentioned anode layer, cathode layer, and solidelectrolyte layer. In the present disclosure, a cathode currentcollector for collecting currents of the cathode layer, and an anodecurrent collector for collecting currents of the anode layer may furtherbe included. Examples of the shape of the current collectors may includea foil shape.

The all solid fluoride ion battery of the present disclosure preferablyincludes a control section that controls charge. The control section,for example, is preferably a control section that controls charge so asthe potential of the anode layer is a potential at which thedefluorination of the M1 element occurs, and at which the defluorinationof the M2 element does not occur. In the present disclosure, thepotential versus Pb/PbF₂ of the anode layer upon charge is preferablycontrolled so as not to be less than −2.5 V. Also, the potential versusPb/PbF₂ of the anode layer upon charge is preferably controlled so as tobe −1.5 V or less.

The control section, for example, may include ECU (Electronic ControlUnit) and PCU (Power Control Unit). The ECU (Electronic Control Unit)sends command (for example, start command or stop command) to the PCU tocharge or discharge based on: the request (for example, charging requestor discharging request) from the outside, and the potential and thevoltage of the all solid fluoride ion battery. The PCU supplies electricpower to the load upon discharge, and receives electric power from thepower source upon charge.

5. All Solid Fluoride Ion Battery

The all solid fluoride ion battery of the present disclosure comprisesat least: a cathode layer, an anode layer, and a solid electrolyte layerformed between the cathode layer and the anode layer. In the presentdisclosure, in the initial state for example, the anode layer includes ametal fluoride containing an M1 element, an M2 element, and a F element;the M1 element is a metal element that fluorination and defluorinationoccur at a potential, versus Pb/PbF₂, of −2.5 V or more; the M2 elementis a metal element that neither fluorination nor defluorination occur ata potential, versus Pb/PbF₂, of −2.5 V or more; and the M2 element is ametal element that, when in a form of a fluoride, fluoride ionconductivity is 1×10⁻⁴ S/cm or more at 200° C. Meanwhile, after chargefor example, the anode layer includes a metal of an M1 element, and ametal fluoride containing an M2 element and a F element, in which themetal of the M1 element and the metal fluoride are dispersed at anatomic level; the M1 element is a metal element that fluorination anddefluorination occur at a potential, versus Pb/PbF₂, of −2.5 V or more;the M2 element is a metal element that neither fluorination nordefluorination occur at a potential, versus Pb/PbF₂, of −2.5 V or more;and the metal fluoride containing the M2 element and the F element hasfluoride ion conductivity of 1×10⁻⁴ S/cm or more at 200° C.

The all solid fluoride ion battery of the present disclosure may be aprimary battery or may be a secondary battery. Among the above, thesecondary battery is preferable, so as to be repeatedly charged anddischarged, and is useful as, for example, a car-mounted battery.Incidentally, the primary battery includes a usage of a secondarybattery as a primary battery (the use for the purpose of just one timedischarge after charge). Also, examples of the shape of the all solidfluoride ion battery of the present disclosure may include a coin shape,a laminate shape, a cylindrical shape, and a square shape.

Incidentally, the present disclosure is not limited to the embodiments.The embodiments are exemplification, and any other variations areintended to be included in the technical scope of the present disclosureif they have substantially the same constitution as the technical ideadescribed in the claim of the present disclosure and offer similaroperation and effect thereto.

EXAMPLES

The present disclosure will be described in more details with referenceto Examples.

Example 1

Synthesis of Metal Fluoride

LaF₃, CaF₂ and BaF₂ were weighed so as to be La:Ca:Ba=76:9:15 in themolar ratio, and mixed by planetary ball milling at revolution of 600rpm for 12 hours. The powder after the ball milling mixture was burnedat 900° C. for 4 hours in an Ar atmosphere to obtainLa_(0.76)Ca_(0.09)Ba_(0.15)F_(2.76). Incidentally, when the burningtemperature is 850° C. or less, there is a possibility that impuritieshaving a fluorite type structure are easily generated; and when over1000° C., there is a possibility that oxide impurities are easilygenerated. Therefore, the burning temperature is preferably within arange of 900° C. to 1000° C., and 900° C. is more preferable.

Production of Measurement Cell

As a solid electrolyte, 150 mg of Ca_(0.6)Ba_(0.4)F₂ was weighed. Theweighed solid electrolyte was subjected to uniaxial pressure moldingunder 1 ton/cm² to obtain a solid electrolyte layer (pressure powdermolded body). On the obtained solid electrolyte layer, 10 mg ofLa_(0.76)Ca_(0.09)Ba_(0.15)F_(2.76) was stacked, and was subjected touniaxial pressure molding under 1 ton/cm² to obtain an anode layer. Asan anode current collector, 3 mg of acetylene black was stacked.

As a cathode layer, a Pb foil was stacked on the surface opposite to thesolid electrolyte layer, and was subjected to uniaxial pressure moldingunder 4 ton/cm² to obtain a cell element. The obtained cell element wasfastened under 6 N·m to obtain a measurement cell. The constitution ofthe measurement cell is shown in FIG. 6. Incidentally, the cathode layeralso provides a function as a cathode current collector.

Example 2

A metal fluoride was obtained in the same manner as in Example 1 exceptthat LaF₃, CaF₂ and BaF₂ were weighed so as to be La:Ca:Ba=90:6:4 in themolar ratio. The composition of the obtained metal fluoride wasLa_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9). Also, a measurement cell was obtainedin the same manner as in Example 1 except that the obtained metalfluoride was used.

Comparative Example 1

A measurement cell was obtained in the same manner as in Example 1except that LaF₃ heat treated at 800° C. was used as the metal fluoride.

Comparative Example 2

A metal fluoride was obtained in the same manner as in Example 1 exceptthat LaF₃ and BaF₂ were weighed so as to be 90:10 in the molar ratio.The composition of the obtained metal fluoride wasLa_(0.9)Ba_(0.1)F_(2.9). A measurement cell was obtained in the samemanner as in Example 1 except that the obtained metal fluoride was used.

Comparative Example 3

An anode mixture was prepared by mixing La_(0.9)Ba_(0.1)F_(2.9) andCa_(0.6)Ba_(0.4)F₂ in a mortar at 9:1 in the weight ratio. The elementratio of this mixture was La:Ca:Ba=76:9:15 in the molar ratio, as inExample 1.

A measurement cell was obtained in the same manner as in Example 1except that the obtained anode mixture was used.

[Evaluation]

Charge and Discharge Test

A charge and discharge test was conducted for each measurement cell. Theconditions for the charge and discharge were: under a vacuum environmentof 1×10⁻³ Pa or less, the measurement cell being heated to 200° C.,within a range of −2.5 V (versus Pb/PbF₂) to −1.5 V (versus Pb/PbF₂),and charge and discharge rate of C/30. The results thereof are shown inFIG. 7 and Table 1. The charging and discharging curves in FIG. 7 showcharging and discharging curves of the anode layers.

TABLE 1 Charging Discharging capacity capacity per weight of per weightof anode layer anode layer Constitution of anode (mAh/g) (mAh/g) Example1 La_(0.76)Ca_(0.09)Ba_(0.15)F_(2.76) 306 223 Example 2La_(0.90)Ca_(0.06)Ba_(0.04)F_(2.9) 309 261 Comparative LaF₃ 76.0 62.4Example 1 Comparative La_(0.90)Ba_(0.1)F_(2.9) 207 161 Example 2Comparative 0.9La_(0.90)Ba_(0.1)F_(2.9) + 262 194 Example 30.1Ca_(0.06)Ba_(0.04)F₂

As shown in FIG. 7 and Table 1, in Examples 1 and 2, the chargingcapacity per weight of each anode layer was confirmed to be a high valuemore than 300 mAh/g. Also, in Examples 1 and 2, the discharging capacityper weight of each anode layer was confirmed to be a high value morethan 200 mAh/g.

In Examples 1 and 2, it is presumed that, upon the initial charge, afluoride ion was desorbed from the LaCaBaF compound, and a state inwhich the La simple substance and the CaBaF compound were dispersed atan atomic level, was formed in the anode layer. Also, it is presumedthat since the fluorination of the La simple substance occurred(functioned as an active material), and a small amount of the CaBaFcompound functioned as a solid electrolyte, the charging capacity andthe discharging capacity were improved.

Meanwhile, it was confirmed that, compared to Examples 1 and 2, thecharging capacity and the discharging capacity were lower in ComparativeExample 1. In Comparative Example 1, upon charge, a fluoride ion wasdesorbed from LaF₃, and only the La simple substance was generated. InComparative Example 1, it is presumed that since the generation reaction(defluorination reaction) of the La simple substance in the anode layerproceeded unevenly, the fluoride ion conductive path in the anode layerwas cut off so that the reaction was intercepted.

Also, it was confirmed that, compared to Examples 1 and 2, the chargingcapacity and the discharging capacity were lower in Comparative Example2. In Comparative Example 2, it is presumed that, upon the initialcharge, the La simple substance and BaF₂ were formed fromLa_(0.9)Ba_(0.1)F_(2.9) in the anode layer. Since the fluoride ionconductivity of BaF₂ is very low such as about 1×10⁻⁹ S/cm at 200° C.,it is presumed that favorable charging capacity and discharging capacitywere not obtained.

Also, it was confirmed that, compared to Examples 1 and 2, the chargingcapacity and the discharging capacity were lower in Comparative Example3. Also, it was confirmed that, compared to Comparative Example 2, thecharging capacity and the discharging capacity were higher inComparative Example 3. In Comparative Example 3, Ca_(0.6)Ba_(0.4)F₂(solid electrolyte) powder was mixed with La_(0.9)Ba_(0.1)F_(2.9) powderso that the composition ratio was made equal to that in Example 1.However, it is presumed that the fluoride ion conductive path could notbe sufficiently secured because of the inferior dispersion of the solidelectrolyte powder in the anode layer.

From the above results, it was confirmed that in Examples 1 and 2, thecapacity property of each all solid fluoride ion battery and thecapacity property of each anode layer could be made favorable comparedto Comparative Examples 1 to 3.

XRD Measurement

Powder XRD measurement was carried out to the metal fluoride in Example2, at the initial state, after the initial charge, and after the initialdischarge. The metal fluoride was filled in an XRD glass holder and wasmeasured using a CuKα ray, within a range of 2θ=10° to 80°, at thescanning rate of 10°/min. The results thereof are shown in FIG. 8.

For the metal fluoride at the initial state, a peak was observed at theposition of 2θ=24.20°, 24.80°, 27.64°, 34.90°, 43.63°, 44.71°, 49.50°,50.48°, and 52.41°. All of these diffraction peaks belong to the peaksof La_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9).

For the metal fluoride after charge, the peaks belonging toLa_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9) were smaller, and the peaks belongingto the La simple substance and the peaks belonging to the solidelectrolyte Ca_((1-x))Ba_(x)F₂, in which 0<x<1, (CaBaF compound) wereobserved. After discharge, the peaks belonging to the La simplesubstance disappeared, and the peaks belonging to LaF₃ and the peaksbelonging to CaBaF compound were observed. Incidentally, the peaksbelonging to LaF₃ were observed at almost the same positions as those ofLa_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9).

From these results, in the anode layer using the metal fluoride ofExample 2, it was confirmed that the metal fluoride was phase split,upon the initial charge, into the La simple substance and the CaBaFcompound, and that irreversible reaction not returning toLa_(0.9)Ca_(0.06)Ba_(0.04)F_(2.9) occurred also after the initialdischarge. In other words, in Example 2, it was confirmed that the metalfluoride containing the M1 element, the M2 element, and the F elementwere phase split, upon the initial charge, into the metal of the M1element and the metal fluoride containing the M2 element and the Felement; the fluorination of the metal of the M1 element phase splitupon the initial discharge occurred so as to form the metal fluoride(M1F) containing the M1 element.

XPS Measurement

XPS measurement was carried out to the metal fluoride in Example 2, atthe initial state, after the initial charge, and after the initialdischarge in order to measure the peaks belonging to the La element, theCa element, the Ba element, and the F element. The results thereof areshown in FIGS. 9A to 9E. As shown in FIGS. 9A to 9E, before and aftercharge and discharge, peak shifts and variations in peak strengthassociated with the oxidation-reduction reaction were observed only forthe La element.

REFERENCE SIGNS LIST

-   1 cathode layer-   2 anode layer-   3 solid electrolyte layer-   4 cathode current collector-   5 anode current collector-   10 all solid fluoride ion battery

What is claimed is:
 1. An all solid fluoride ion battery comprising: acathode layer, an anode layer, and a solid electrolyte layer formedbetween the cathode layer and the anode layer; wherein the anode layerincludes a metal fluoride containing an M1 element, an M2 element, and aF element; the M1 element is a metal element that fluorination anddefluorination occur at a potential, versus Pb/PbF₂, of −2.5 V or more;the M2 element is a metal element that neither fluorination nordefluorination occur at a potential, versus Pb/PbF₂, of −2.5 V or more;the M2 element is a metal element that, when in a form of a fluoride,fluoride ion conductivity is 1×10⁻⁴ S/cm or more at 200° C.; a contentof the metal fluoride to a total weight of the anode layer is 70% byweight or more; and the M2 element contains metal elements of two kindsor more.
 2. The all solid fluoride ion battery according to claim 1,wherein the metal fluoride has a composition represented byM1_(x)M2_((1-x))F_(y), in which 0.75≤x≤0.95 and y is a real number morethan
 0. 3. The all solid fluoride ion battery according to claim 1,wherein the M1 element is a metal element that fluorination anddefluorination occur at a potential, versus Pb/PbF₂, of −1.5 V or less.4. The all solid fluoride ion battery according to claim 1, wherein theM1 element contains at least one of a La element and a Ce element. 5.The all solid fluoride ion battery according to claim 1, wherein the M2element contains at least two kinds of a Ca element, a Ba element, a Lielement, a Sr element, and a Y element.
 6. The all solid fluoride ionbattery according to claim 1, wherein the content of the metal fluorideto the total weight of the anode layer is 90% by weight or more.
 7. Theall solid fluoride ion battery according to claim 1, wherein the contentof the metal fluoride to the total weight of the anode layer is 100% byweight.
 8. The all solid fluoride ion battery according to claim 1,wherein the M1 element contains a La element, and the M2 elementcontains a Ca element and a Ba element.